"D region." YourDictionary, n.d. Web. 23 October 2018. <https://www.yourdictionary.com/d-region>.
D region. (n.d.). Retrieved October 23rd, 2018, from https://www.yourdictionary.com/d-region
The region of the atmosphere that lies in the upper mesosphere, extending from about 70 to 90 km (43 to 56 mi) above the Earth. The D region is responsible for the daytime absorption of high-frequency radio signals; at night, oxygen ions recombine with free electrons and form oxygen molecules that are transparent to such signals, which bounce off of the E region and back to Earth. Also called D layer